1. Field of the Invention
The present invention relates to a screen printing method and a screen printing apparatus primarily for printing a print-use paste, such as solder paste or pastes for thick-film circuit formation, onto a board, such as a printed circuit board, for electronic circuit formation.
2. Description of the Related Art
In recent years, screen printing apparatuses have been used for the solder paste printing process in circuit assembly processes of electronic components, or the like. As the board for electronic circuit formation is advanced toward a further fine structure with the miniaturization of electronic equipment, there has been a demand for higher precision of printing with solder paste or the like responsively.
FIG. 16 shows a conventional screen printing apparatus.
A print-object article (article to be printed) 1 is positioned and fixed to a positioning stage 2 that can be ascended and descended by a positioning stage ascent/descent driving means 3. For printing process, the positioning stage 2 is lifted by the positioning stage ascent/descent driving means 3 to such an extent that the top surface of the print-object article 1 comes in near contact with the bottom surface of a stencil 4.
A left-squeegee ascent/descent driving means 6a and a right-squeegee ascent/descent driving means 6b, which are commonly implemented by double-rod air cylinders, have squeegees 5a, 5b attached to their ends. Lower-limit positions of the squeegees 5a, 5b, (i.e., the push-in strokes to the stencil 4) are set by positional adjustment of stoppers 7a, 7b. A drive source for a horizontal reciprocation driving means 8 is commonly an AC servo motor. In the state that the left squeegee 5a and the right squeegee 5b have descended into contact with the top surface of the stencil 4, the horizontal reciprocation driving means 8 moves the left squeegee 5a and the right squeegee 5b horizontally (in the X-direction), so that a print paste 9, such as solder paste, is moved on the top surface of the stencil 4 by the left squeegee 5a and the right squeegee 5b. 
The printing process is carried out as shown in FIG. 17.
At the first step, the print-object article 1 is positioned and fixed to the positioning stage 2. At the second step, the print-object article 1 is lifted to a proximity of the bottom surface of the stencil 4. The left squeegee 5a is lowered at the third step, and the left squeegee 5a is moved rightward in the X-direction at the fourth step, by which printing is executed.
Thereafter, the print-object article 1 is separated away from the stencil 4 at a low speed (20 mm/sec) at the fifth step, the left squeegee 5a is lifted at the sixth step, and the print-object article 1 is removed at the seventh step.
Next, a printing operation on the right squeegee 5b side is also executed in the same way as above, and the operation is then alternately repeated.
The drive source for the positioning stage ascent/descent driving means 3 is commonly an air cylinder, pulse motor, AC servo motor, or the like. Among these, the AC servo motor is particularly suitable, because low-speed descent of the driving means 3 allows an easy accomplishment of high-precision printing results with less spread and blurs (i.e., less making indistinct and hazy in outline). The left squeegee 5a and the right squeegee 5b are given mainly by elastic material, commonly urethane rubber (hardness: Hs 60-90xc2x0).
In this way, successful prints free from spread and blurs can be obtained continuously. However, there are issues as shown in FIGS. 18A to 18C.
FIG. 18A shows a completion state of the fourth step, FIG. 18B shows an early-stage state of the fifth step, and FIG. 18C shows a last-stage state of the fifth step. In the completion state of the fourth step as shown in FIG. 18A, a print pattern 11a has been formed with relatively good precision. In this state, the left squeegee 5a is curved only by a portion corresponding to the push-in stroke into the stencil 4.
In FIG. 18B, the left squeegee 5a pushes down the stencil 4 to an extent of the push-in stroke, so that the stencil 4 is tilted, causing the print pattern to gradually collapse as shown by a print pattern 11b. As a result, as shown in FIG. 18C, a horn 10 with the print paste 9 lifted is formed at a corner portion of a print pattern 11c. 
The horn 10 of the print paste 9 would gradually bow, and drop onto the print-object article 1, causing printing faults as an issue.
As an example, in electronic component assembling processes typified by solder paste printing, the solder paste bowed and dropped after the subsequent-process soldering reflow would cause soldering faults such as solder balls and solder bridges.
In recent years, in the fields of screen printing methods and apparatuses therefor, there have increasingly been cases where screen printing is executed on boards on which an area corresponding to a large opening area of a screen metal mask (stencil) and an area corresponding to a minute opening area thereof are mixedly present in circuits. The term xe2x80x9cminute opening areaxe2x80x9d refers to an area where the value of each opening size of openings of the mask along the squeegee""s moving direction is smaller than a specified threshold. The term xe2x80x9clarge opening areaxe2x80x9d refers to an area where the value of each opening size of openings of the mask along the squeegee""s moving direction is not smaller than a specified threshold.
Now a case where a board in which an area corresponding to a large opening area of the mask and an area corresponding to a minute opening area thereof are mixedly present in circuits is screen-printed by a conventional screen printing method and apparatus therefor is described with reference to FIGS. 19 to 22.
Referring to FIG. 19, which is a perspective view of the screen printing apparatus, reference numeral 101 denotes a screen metal mask; 102 denotes a board; 803 denotes a print head; 104 denotes a print-head-use AC servo motor for driving the print head 803; 105 denotes a print-head-use ball screw for transferring the driving force of the print-head-use AC servo motor 104; 106 denotes a print-head-use AC servo driver for driving the print-head-use AC servo motor 104; 107 denotes a visual recognition camera for recognizing recognition marks of the screen metal mask 101 and the board 102; 108 denotes a recognition-camera-use AC servo motor for driving the visual recognition camera 107; 109 denotes a recognition-camera-use ball screw for transferring the driving force of the recognition-camera-use AC servo motor 108; 110 denotes a recognition-camera-use AC servo driver for driving the recognition-camera-use AC servo motor 108; 811 denotes a controller for issuing commands to the individual servo motor drivers; 112 denotes a control panel for entering data into the controller 811; 113 denotes a stage for restricting the board 102; 114 denotes a stage-use AC servo motor for driving the stage 113; 115 denotes a stage-use ball screw for transferring the driving force of the stage-use AC servo motor 114; 116 denotes a stage-use AC servo driver for driving the stage-use AC servo motor 114; 117 denotes a loader for carrying in the unprinted board 102; 118 denotes an unloader for carrying out the printed board 102; and 119 denotes the main unit of the screen printing apparatus.
Referring to FIG. 20, which is a plan view of the screen metal mask 101, reference numeral 120 denotes a large opening area where solder paste in large openings of the mask 101 are printed on the board 102 (e.g. an area corresponding to a chip component area of the board 102) and 121 denotes a minute opening area, where solder paste in minute openings of the mask 101 are printed on the board 102 (e.g. an area corresponding to a narrow-pitch QFP (Quad Flat Package) area of the board 102).
The operation of the screen printing apparatus which employs a conventional screen printing method is explained with reference to FIGS. 19 to 22.
At Step #901 of FIG. 22, which shows the flow chart of the conventional example, an operator, with the use of the control panel 112, enters descent/ascent positions, i.e. a print start position and a print end position, of a squeegee 123 of the print head 803 in accordance with the screen metal mask 101, and enters a print speed V that allows the circuits of the board 102 to be printed stably and appropriately. In this case, the print speed V that allows a stable and an appropriate printing becomes such a low print speed that printing can be stably and appropriately performed on areas out of the circuits constituting the board 102 which correspond to most minute opening areas of the mask.
At Step #902, the loader 117 carries the board 102 into the stage 113.
At Step #903, the visual recognition camera 107 recognizes the position of the recognition mark of the board 102, performs a calculation of positional correction amount based on the position of the recognition mark of the screen metal mask 101, and performs the correction for the positioning of the board 102.
At Step #904, the squeegee 123 of the print head 803 moves and descends to the print start position, prints from the print start position to the print end position at the same print speed V entered at Step #901, and ascends.
At Step #905, the stage 113 on which the board 102 is placed descends so that the board 102 is transferred to the unloader 118, and the unloader 118 carries the board 102 out of the screen printing apparatus main unit 119.
However, in this conventional construction, since the speed of the squeegee 123 is constant, such a low print speed that printing can be appropriately performed on areas among the circuits constituting the board 102 which correspond to most minute opening areas of the mask is employed as the speed that allows the whole circuits of the board 102 to be printed stably and appropriately.
The reason of this is that, in the printing using the squeegee 123, if the minute opening area 121 of the screen metal mask 101 as shown in FIG. 20 was printed at a high print speed suitable for the large opening area 120 of the screen metal mask 101, as shown in FIG. 21A, the speed V of the squeegee 123 would be so fast that solder paste 122 could not fill the interior of a print hole 124 of the screen metal mask 101 positioned onto an electrode 125 of the board 102 and that, as a result, the quantity of the solder paste 122 to be printed on the electrode 125 of the board 102 would lack after the removal of the screen metal mask 101, as shown in FIG. 21B.
Accordingly, for the conventional printing apparatus, when the large opening area 120 and the minute opening area 121 are mixedly present, there is an issue that a longer process time for printing would be required because the low print speed for the minute opening area 121 is used even for the large opening area 120 that could be printed at the high print speed.
Another conventional example is explained with reference to FIGS. 12 to 14 and 23 showing a screen printing apparatus, as well as to FIG. 24 showing the flow chart of a conventional printing method.
The stage 2, on which a print-target article such as a printed circuit board 1 carried in from the preceding step is placed and positionally restricted, ascends up to the bottom surface of the stencil 4. After the printing, the stage 2 descends so that the printed circuit board 1 is carried out to the subsequent step. The leftward-printing squeegee 5a and the rightward-printing squeegee 5b are moved up and down by a squeegee ascent/descent driving means, while the squeegees 5a, 5b are also moved rightward and leftward by a horizontal mover 8c having a nut screwed to a screw shaft 8b with the screw shaft 8b being rotated as the motor 8a of the horizontal reciprocation driving means 8 rotates. As a result, the solder paste 9, which is an example of the print paste, placed on the stencil 4 is printed onto the printed circuit board 1 via the stencil 4. FIGS. 12 and 13 each show a state during a rightward printing process, and FIG. 14 shows a leftward-printing standby state. Reference numeral 812 in FIG. 23 denotes an NC unit that issues a command for driving the motor 8a, and 811 denotes a controller for controlling the whole printing apparatus.
Next, the operation of the conventional example is explained with reference to the flow chart of FIG. 24 as well as FIGS. 12 to 14 and 23.
First, a preset print speed V (mm/sec) is entered from the controller 811 to the NC unit 812 as the moving speed of the squeegee. This allows the NC unit 812 to control the motor 8a so that the left and right squeegees 5a, 5b move at the input print speed V.
At Step #101, a printed circuit board carry-in step, of FIG. 24, the printed circuit board 1 carried in from the preceding step is placed and positionally restricted on the stage 2, in which state the stage 2 ascends so that the top surface of the printed circuit board 1 placed thereon is put into contact with the bottom surface of the stencil 4.
At Step #102, a printing step, as described above, the motor 8a rotates under the control of the NC unit 812, so that the left squeegee 5a or the right squeegee 5b moves at the print speed V, by which the solder paste 9 placed on the stencil 4 is passed through the stencil 4 so as to be printed on the printed circuit board 1. In this process, it is an optimum state that the solder paste 9, during the printing process, be pressed by the squeegee 5a so as to roll and move on the stencil 4 (i.e., that the solder paste 9 be in a rolling state). Such a state of the solder paste 9 results in a successful printed pattern as well as a good screen-pass performance.
At Step #103, a printed circuit board carry-out step, upon completion of the printing, the motor 8a halts, the left squeegee 5a ascends, the stage 2 lowers, and the printed circuit board 1 is carried out to the subsequent step.
At Step #104, a decision step, it is decided whether or not the planned number of works has been completed. If it has not, the program returns to Step #101, and if it has been completed, the program comes to an end.
However, with this conventional constitution, there may occur print standby time durations due to the circumstances of the preceding and subsequent steps in which the printed circuit board 1 is carried in or out, or to rest time and the like. Then, a prolonged print standby time would cause the thixotropy ratio of the solder paste 9 to be lowered and the solder paste 9 placed on the stencil 4 to be dried such that its viscosity would increase. In this state of the solder paste 9, with the print standby canceled, when the printed circuit board 1 is carried in and positioned so that the printing is started, the left squeegee 5a moves at the print speed V previously entered to the NC unit 812. In this state, the solder paste 9, whose thixotropy ratio has decreased and whose viscosity also has increased, would be printed in a state other than appropriate rolling. This would cause the occurrence of such faults as solder paste chipping, solder shortages, or blurs, posing an issue that defective boards may be produced.
An object of the present invention is to provide a screen printing method and a screen printing apparatus capable of printing with good print quality.
More specifically, an object of the present invention is to provide a screen printing method and a screen printing apparatus capable of achieving a good printing result in which the corner portions of the print paste are prevented from the formation of horns. Another object of the present invention is to provide a screen printing method and an apparatus therefor capable of printing, with solder paste, boards in which areas corresponding to a large opening area and a minute opening area of a screen metal mask (stencil) are mixedly present, with high quality and high efficiency. A further object of the present invention is to provide a printing method and a printing apparatus in which such faults as solder paste chipping, solder shortages, or blurs will not occur when the print standby state is canceled and the printing process is resumed.
According to a first aspect of the present invention, there is provided a screen printing method for printing a circuit pattern corresponding to a circuit pattern of a stencil, onto a print-object article placed on an ascendable/descendable positioning stage, through a step of moving a squeegee horizontally while the squeegee is pushed in on a top surface of the stencil having the circuit pattern formed thereon so that print paste is printed and applied to the print-object article via the stencil, the screen printing method comprising steps of:
lifting the squeegee at least to an extent of a push-in stroke, to which the squeegee has been pushed in on the stencil; and
thereafter, separating the print-object article away from a bottom surface of the stencil by moving the positioning stage downward.
According to a second aspect of the present invention, there is provided the screen printing method according to the first aspect, in which an ascent standby position of the squeegee above the stencil prior to the pushing-in, a push-in position of the squeegee to the stencil, and a momentary position at which the squeegee is present at a moment when the squeegee makes contact with the top surface of the stencil are entered each in numerical value into a controller of a screen printing apparatus, and in which the controller makes the following specified operations executed at the positions entered in numerical value, the screen printing method comprising, before the lifting and separating steps, steps of:
keeping the squeegee on standby at the ascent standby position before a start of the screen printing; and
lowering the squeegee from the ascent standby position to the push-in position, and making the squeegee execute the push-in operation to thereby execute a printing operation,
wherein in the lifting step, upon completion of the printing operation, the squeegee is lifted from the push-in position to the momentary position at which the squeegee is present at a moment when the squeegee makes contact with the top surface of the stencil.
According to a third aspect of the present invention, there is provided the screen printing method according to the first or second aspect, wherein the squeegee is moved up and down relative to the stencil by digital control.
According to a fourth aspect of the present invention, there is provided a screen printing apparatus for printing a circuit pattern corresponding to a circuit pattern of a stencil, onto a print-object article,
the apparatus comprising:
an ascendable/descendable positioning stage for placing the print-object article thereon, moving the print-object article upward, and moving the print-object article downward so as to separate the print-object article away from a bottom surface of the stencil;
a squeegee for moving horizontally while the squeegee is pushed in on a top surface of the stencil having the circuit pattern formed thereon so that print paste is printed and applied to the print-object article via the stencil, the squeegee being lifted at least to an extent of a push-in stroke, to which the squeegee has been pushed in on the stencil; and
a controller for controlling a squeegee ascent/descent driving unit and a positioning stage ascent/descent driving unit in such a way that after the squeegee is lifted at least to the extent of the push-in stroke, the print-object article is separated away from the bottom surface of the stencil by moving the positioning stage downward.
According to a fifth aspect of the present invention, there is provided the screen printing apparatus according to the fourth aspect, in which an ascent standby position of the squeegee above the stencil prior to the pushing-in, a push-in position of the squeegee to the stencil to which the squeegee has been pushed in on the stencil, and a momentary position at which the squeegee is present at a moment when the squeegee makes contact with the top surface of the stencil are entered each in numerical value from an input means into the controller, and in which the controller makes the following specified operations executed at the positions entered in numerical value, wherein
the squeegee is brought and kept on standby at the ascent standby position by the squeegee ascent/descent driving unit before a start of the screen printing;
the squeegee is lowered from the ascent standby position to the push-in position by the squeegee ascent/descent driving unit, and the squeegee is made to execute the push-in operation to thereby execute a printing operation;
upon completion of the printing operation, when the squeegee is lifted to the extent of the push-in stroke, the squeegee is lifted by the squeegee ascent/descent driving unit from the push-in position to the momentary position at which the squeegee is present at a moment when the squeegee makes contact with the top surface of the stencil; and
the positioning stage is lowered by the positioning stage ascent/descent driving unit so as to separate the print-target article away from the bottom surface of the stencil.
According to a sixth aspect of the present invention, there is provided the screen printing apparatus according to the fourth or fifth aspect, wherein the squeegee ascent/descent driving unit comprises a motor, a screw shaft connected to a rotary shaft of the motor, and a mover which is screwed to the screw shaft and which moves the squeegee along upward and downward directions, wherein the upward and downward movement of the squeegee is controlled by rotational control of the motor.
According to a seventh aspect of the present invention, there is provided the screen printing apparatus according to any one of the fourth through sixth aspects, wherein the squeegee is moved up and down relative to the stencil by digital control with the controller.
According to an eighth aspect of the present invention, there is provided the screen printing apparatus according to any one of the fourth through seventh aspects, wherein after the squeegee is lifted by the squeegee ascent/descent driving unit at least to the extent of the push-in stroke, to which the squeegee has been pushed in on the stencil, the positioning stage moves downward by the positioning stage ascent/descent driving unit at a speed slower than a speed at which the squeegee is lifted, whereby the print-object article is separated away from the bottom surface of the stencil, and thereafter the squeegee is lifted up to its standby position by the squeegee ascent/descent driving unit.
According to a ninth aspect of the present invention, there is provided a screen printing method for printing, with use of a screen printing apparatus, solder paste on an electrode of a board to be printed, by positioning a screen mask onto the board and by printing the solder paste supplied onto the screen mask into the screen mask with a squeegee of a print head which moves parallel to the screen mask while being kept in contact with the screen mask, wherein the board is classified into a first area where a value of each of opening sizes of the mask along a direction in which the squeegee moves is smaller than a specified threshold, and a second area where a value of each of opening sizes of the mask is not smaller than the threshold, and a speed of the squeegee at the first area is made slower than a speed of the squeegee at the second area.
According to a tenth aspect of the present invention, there is provided the screen printing method according to the ninth aspect, further comprising steps of:
entering data of the first area and the second area as well as data of the squeegee speeds corresponding to the first area and the second area, into the screen printing apparatus by an operator or from a higher-order computer that controls the screen printing apparatus; and
switching the squeegee speed between the first and second areas based on the entered data of the first area and the second area as well as the data of the squeegee speeds corresponding to the first area and the second area.
According to an 11th aspect of the present invention, there is provided the screen printing method according to the ninth aspect, further comprising steps of:
entering data of the first area and the second area into the screen printing apparatus by recognizing the opening sizes of the mask by a visual recognition camera, and entering into the screen printing apparatus data of the squeegee speeds corresponding to the first area and the second area by an operator or a higher-order computer that controls the screen printing apparatus; and
switching the squeegee speed between the first and second areas based on the entered data of the first area and the second area by the recognition of the visual recognition camera and the entered data of the squeegee speeds corresponding to the first area and the second area by the operator or the higher-order computer.
According to a 12th aspect of the present invention, there is provided the screen printing method according to any one of the 9th to 11th aspects, wherein when openings where a value of each of opening sizes of the mask along the squeegee""s moving direction is smaller than a specified threshold and openings where a value of each of opening sizes of the mask along the squeegee""s moving direction is not smaller than the specified threshold are mixedly present along a direction intersecting the squeegee""s moving direction, the squeegee is moved at the speed corresponding to the first area by assuming as the first area based on the smaller opening sizes.
According to a 13th aspect of the present invention, there is provided the screen printing method according to any one of the 9th to 12th aspects, wherein when external terminals of components to be mounted to the board are placed on the solder paste formed by the printing, the threshold is a pitch between the external terminals.
According to a 14th aspect of the present invention, there is provided a screen printing apparatus for printing solder paste on an electrode of a board to be printed, by positioning a screen mask onto the board and by printing the solder paste supplied onto the screen mask into the screen mask with a squeegee of a print head which moves parallel to the screen mask while being kept in contact with the screen mask, the screen printing apparatus comprising:
a controller for executing control process in such a way that the board is classified into a first area where a value of each of opening sizes of the mask along a direction in which the squeegee moves is smaller than a specified threshold, and a second area where a value of each of opening sizes is not smaller than the threshold, and that a speed of the squeegee at the first area is made slower than a speed of the squeegee at the second area.
According to a 15th aspect of the present invention, there is provided the screen printing apparatus according to the 14th aspect, wherein data of the first area and the second area as well as data of the squeegee speeds corresponding to the first area and the second area are entered into the controller by an operator or a higher-order computer that controls the controller, and wherein the squeegee speed is switched between the first and second areas by the controller based on these entered data.
According to a 16th aspect of the present invention, there is provided the screen printing apparatus according to the 14th aspect, further comprising a visual recognition camera for recognizing a state of openings of the mask, wherein data of the first area and the second area are entered into the controller by the visual recognition camera recognizing the openings of the mask, and data of the squeegee speeds corresponding to the first area and the second area are entered by an operator or a higher-order computer that controls the controller, and wherein the squeegee speed is switched between the first and second areas by the controller based on these entered data.
According to a 17th aspect of the present invention, there is provided the screen printing apparatus according to any one of the 14th to 16th aspects, wherein when openings where a value of each of opening sizes of the mask along the squeegee""s moving direction is smaller than a specified threshold and openings where a value of each of opening sizes of the mask along the squeegee""s moving direction is not smaller than the specified threshold are mixedly present along a direction intersecting the squeegee""s moving direction, the controller makes the squeegee move at the speed corresponding to the first area by assuming as the first area based on the smaller opening sizes.
According to an 18th aspect of the present invention, there is provided the screen printing apparatus according to any one of the 14th to 17th aspects, wherein when external terminals of components to be mounted to the board are placed on the solder paste formed by the printing, the threshold is a pitch between the external terminals.
According to a 19th aspect of the present invention, there is provided the screen printing apparatus according to any one of the 14th to 18th aspects, further comprising:
a loader for carrying in a board on which the solder paste is to be printed;
a stage for holding the board, which has been carried in by the loader, to perform screen printing on the board; and
an unloader for carrying out the board, on which the solder paste has been printed, from the stage,
the controller comprising:
storage means for storing data for classifying the board into the first area where the value of each of the opening sizes of the mask along the direction in which the squeegee moves is smaller than the specified threshold,
and the second area where the value of each of the opening sizes is not smaller than the threshold, data of the squeegee speed at the first area, and data of the squeegee speed at the second area slower than the squeegee speed at the first area; and
program generating means for generating a program by which the squeegee speed of the print head is switched on the way of a printing process based on the data stored in the storage means, and the print head comprising squeegee-speed on-process switching means for switching the squeegee speed on the way of the printing process based on control of the controller in accordance with the program.
According to a 20th aspect of the present invention, there is provided a screen printing method for screen printing solder paste at a reference print speed by using a squeegee, the screen printing method comprising:
a step for, upon an occurrence of print standby time during a printing operation, measuring the print standby time; and
a step for, at a resumption of printing with the print standby canceled, screen-printing the solder paste placed on a screen mask during the standby time, by moving the squeegee at an adjusted print speed lower than the reference print speed based on a relationship between the print standby time and a print time due to the adjusted print speed after the resumption of printing.
According to a 21st aspect of the present invention, there is provided the screen printing method according to the 20th aspect, wherein a time for which the screen printing is executed at the adjusted print speed is set according to a resupply amount of the solder paste.
According to a 22nd aspect of the present invention, there is provided the screen printing method according to the 20th or 21st aspect, wherein over a specified time elapse after the screen printing is started at the adjusted print speed, the screen printing is executed at the reference print speed.
According to a 23th aspect of the present invention, there is provided the screen printing method according to the 20th or 21st aspect, wherein upon completion of the screen printing of a specified number of boards after the screen printing is started at the adjusted print speed, the screen printing is executed at the reference print speed.
According to a 24th aspect of the present invention, there is provided the screen printing method according to any one of the 20th to 23rd aspects, wherein the adjusted print speed until the print speed is returned to the reference print speed is set into a plurality of steps.
According to a 25th aspect of the present invention, there is provided a screen printing apparatus for screen printing solder paste at a reference print speed by using a squeegee, the screen printing apparatus comprising:
a controller for, upon an occurrence of print standby time during a printing operation, measuring the print standby time, and for, at a resumption of printing with the print standby canceled, screen-printing the solder paste placed on a screen mask during the standby time, by moving the squeegee at an adjusted print speed lower than the reference print speed based on a relationship between the print standby time and a print time due to the adjusted print speed after the resumption of printing.
According to a 26th aspect of the present invention, there is provided the screen printing apparatus according to the 25th aspect, wherein, by the controller, a time for which the screen printing is executed at the adjusted print speed is set according to a resupply amount of the solder paste.
According to a 27th aspect of the present invention, there is provided the screen printing apparatus according to the 25th or 26th aspect, wherein, by the controller, over a specified time elapse after the screen printing is started at the adjusted print speed, the screen printing is executed at the reference print speed.
According to a 28th aspect of the present invention, there is provided the screen printing apparatus according to the 25th or 26th aspect, wherein, by the controller, upon completion of the screen printing of a specified number of boards after the screen printing is started at the adjusted print speed, the screen printing is executed at the reference print speed.
According to a 29th aspect of the present invention, there is provided the screen printing apparatus according to any one of the 25th to 28th aspects, wherein, by the controller, the adjusted print speed until the print speed is returned to the reference print speed is set into a plurality of steps.
According to the screen printing method of the present invention, before separating the print-object article downward away from the bottom surface of the stencil with the positioning stage, the squeegee can be lifted at least to the extent of a push-in stroke, to which the printing squeegee has been pushed in on the stencil, and thereafter the print-object article can be separated downward away from the bottom surface of the stencil with the positioning stage, and after that, the printing squeegee can be lifted. Therefore, the print-object article can be separated from the stencil while the stencil is kept horizontal without being tilted. Thus, a successful print pattern generally equal to the circuit pattern provided on the stencil and having, at the corner portions, no such horns as has been involved in the conventional method can be obtained.
According to the screen printing apparatus of the present invention, the apparatus is provided with a controller for operating the printing squeegee ascent/descent driving unit and the positioning stage ascent/descent driving unit in such a way that, after the squeegee is lifted before separating the print-object article away from the bottom surface of the stencil by moving the positioning stage downward, the print-object article is separated away from the bottom surface of the stencil by moving the positioning stage downward. Therefore, the screen printing method of the present invention can be realized, so that similar effects can be produced.
In the screen printing method of the present invention and the screen printing apparatus of the invention, the controller additionally comprises: storage means for entering thereto and storing therein data relating to the settings of the large opening area and the minute opening area of the board, as well as data relating to the setting of a high squeegee speed for the large opening area and to the setting of a low squeegee speed for the minute opening area; and program generating means for generating a program by which the squeegee speed of the print head is switched on the way of a printing process based on the entered data. Further, the print head additionally comprises squeegee-speed on-process switching means for switching the squeegee speed on the way of the printing process. Therefore, by performing the input of large opening area and minute opening area as well as the input of high squeegee speed and low squeegee speed by the operator or the higher-order (host) computer that controls the screen printing apparatus, or by performing the input of large opening area and minute opening area by the recognition of the visual recognition camera as well as the input of high squeegee speed and low squeegee speed by the operator or the higher-order (host) computer, the areas where only the areas corresponding to the large opening areas of the mask are present in the board at which the print paste is to be printed are printed at the high squeegee speed while the areas where only the areas corresponding to the minute opening areas of the mask are present in the board at which the print paste is to be printed are printed at the low squeegee speed. Thus, it is enabled to maintain a high print quality and to ensure a high productivity when the large opening area and the minute opening area are mixedly present.
According to the screen printing method of the present invention, at a resumption of printing, in order that the print paste placed on the stencil during the standby time can be printed while appropriately rolling, an adjusted print speed lowered below the reference print speed is set in accordance with a change in the print paste characteristic that is discriminated based on the measured print standby time. Therefore, even if the print paste has changed in characteristic due to, for example, drying during the print standby time, printing at the adjusted print speed allows the print paste to be printed while appropriately rolling. Thus, the occurrence of such faults as print paste chipping, print paste shortages, and blurs can be eliminated.
Also, the number of adjusted prints to be printed at the adjusted print speed is set responsive to a resupply amount of new print paste, and the print speed is returned to the reference print speed after the number of adjusted prints have been printed at the adjusted print speed. Therefore, the print speed can be returned to the reference print speed without causing any faults such as print paste chipping, print paste shortages, and blurs.
According to the printing method of the present invention, a one-step adjusted print speed may properly be employed a for short print standby time, and the number of steps of adjusted print speed may be increased as the print standby time becomes longer. Therefore, a wide range of short to long print standby times can be handled successfully.